A design engineer wants to construct a sample mean chart for controlling the service life of a halogen headlamp his company produces. He knows from numerous previous samples that this service life is normally distributed with a mean of 500 hours and a standard deviation of 20 hours. On three recent production batches, he tested service life on random samples of four headlamps, with these results: Sample SERVICE LIFE 49 525 470 500 515 480 505 500 505 513 460 470 1. What is the sample mean service life for sample 2?
A) 460 hours
B) 495 hours
C) 515 hours
D) 525 hours
2. What is the mean of the sampling distribution of sample means for whenever service life is in control?
A) 250 hours
B) 470 hours
C) 495 hours
D) 500 hours
E) 515 hours
3. If he uses upper and lower control limits of 520 and 480 hours, on what sample(s) (if any) does service life appear to be out of control?
A) sample 1
B) sample2
C) sample 3
D) both samples 2 and 3
E) all samples are in control